Page 183 - Photodetection and Measurement - Maximizing Performance in Optical Systems

Stability and Tempco Issues

176 Chapter Eight

Cube Parallel plate Thick plate Pellicle

Angled
Beams Absorber Beams
overlap Beams displaced overlap
laterally
Wedge Wollaston Grating Actuated
+1
p
s
Orthogonal -1
polarizations
Beams displaced
in angle
Fused fiber

Figure 8.13 Selection of beam-splitters used for intensity referencing.

Amplitudes
Maximum intensity 1 n 1 n 2
2 2
|A | + |A | + 2|A ||A | f
1
2
1
2
Intensity 4|A | |A | |A | e j 1
1
f
2 2 1 2 |A | e j 2
|A | + |A | 2
2
1
Mean
Minimum intensity
2 2
|A | + |A | – 2|A ||A |
2
1
2
1
n - n 2
1
|A | =
1
n + n 2
1
Phase Difference D = f – f Amplitude reflection coefficient
1
2
at normal incidence
Air/glass: |A 1 | = 0.2
Figure 8.14 Coherent reflection addition in beam-splitters can lead to large intensity split-ratio fluc-
tuations, even with small intensity reflection coefficients.
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